Composite radius block



J. W. BARNHILL COMPOSITE RADIUS BLOCK f Jan. 21, 1964 2 Sheets-Sheet l Filed April 10, 1961 IN VEN TOR. J.W. BARN HILL ATTORNEY Filed April 10, 1961 2 Sheets-Sheet 2 wwwl V 30 INVENTOR.

J.W. BARNHILL MZ-M ATTORNEY United States Patent 3,118,488 C'QMPOSITE RADIUS BLOCK James W. Barnhiil, Lemon Grove, Calif., assignor to Ruhr Corporation, a corporation of California Filed Apr. 10, 1961, Ser. No. 191,848 8 Claims. (Cl. 153-40) This invention relates generally to machines for bending thin wall metallic tubing and more particularly to improvements per se in the bending mechanisms conventionally employed in such machines and which principally comprise two relatively movable die parts sometimes referred to hereinafter as a composite radius block.

The bending of thin wall metallic tubing, particularly where the radius of bend is tight, or close, cannot normally be accomplished without great difficulty in view of the tendency of the tubing to wrinkle in the region of the inner radius of the bent portion of the tubing and/or to become oval or generally out of round both in circular cross section and in circular arc in the region of the outer radius of the bent portion of the tubing. Such tubular imperfections inherently reduce the strength and cross sectional area of the tubing in the region of bend thereof and introduce objectional internal surface irregularities and roughness which impede and obstruct the normal flow of fluids through the bent tubing.

These difficulties have been obviated to some extent in the present state of the tube bending art through the use of relatively rotatable bending dies which conform closely to the outer circular surface of the tubing and which, in their operation on the tubing to bend the same, provide a combined drawing, wiping and wrapping action thereon. This action is supplemented, further, through the use internally of a flexible mandrel which conforms to the inner circular surface of the tubing. In forming the bend in the tubing by these prior art means, the same is firmly held slidably against the stationary or fixed conforming die and clamped at the free end thereof, to the rotary die for rotation therewith, upon rotation of the latter, the tubing is drawn in a wiping action over the mandrel internally, and externally over and with respect to the conforming surface of the fixed die in the region of tangency thereof. As the tubing is thusly drawn and wiped in the region of tangency, the same is caused simultaneously to bend and conform to the curved or arcuate portion of the conforming surface of the rotary die in a generally wrap around action thereon.

To this end, the tubing must be firmly held and, accordingly, the bending dies are carefully designed and machined so as to closely conform and constrain the tubing to its circular cross section, particularly within the region of initial bending of the tube, that is, at the point of tangency between the remaining straight or unbent portion of the tube and that bent portion thereof which is constrained to follow the arc and curvature of the rotary bending die. It is within this region of initial bending that the internal mandrel functions to constrain the tubing to its inner circular cross section. As a result, great pressures are brought to bear between the adjoining mandrel, tubing, and die surfaces in this region of tangency and great force and considerable power is required to move and wipe the tubing axially of the mandrel and with respect to the fixed forming die as the tube moves, as required, to form the bend.

In order to follow the bending movements, various prior art structural arrangements are provided and available to give the mandrel inherent flexibility such, for example, as by forming the mandrel of a number of interconnected ball segments which tend to preserve and restore the circular cross section of the tubing as the same is drawn over the mandrel in the process of forming the bend, the mandrel being fastened to the bending machine 3,1l8A88 Patented Jan. 21, 1964 and therefore held against movement. The tubing tends to move out of round as it passes between the axially spaced ball segments but the wiping action of the ball surfaces on this deformed portion of the tubing tends to restore the same to circular cross section in the process of being forcibly drawn in succession over the interconnected ball segments which may number two or more. Again, considerable force is required to effect this wiping action and this condition becomes aggravated by any failure of the conforming dies to constrain the tubing to its circular cross section inasmuch as the pressures on the ball segments are transferred to the adjoining tube portions to force the same into any irregularities in the die surfaces.

In certain prior art arrangements, for example, it is found that the wiper die, which is held stationary to the bending machine, and to which the unformed length of the tubing is slidably constrained and conformed, must present to the tubing, a supporting surface which extends to the point of tangency with the rotary die. This entails the precision forming of a feathered edge on the wiper die so that its support surface merges smoothly into that of the rotary die against which and to which the formed and curved end portion of the tubing is wrapped and clamped. In the use of this arrangement, particularly where tight bends are to be formed, that is to say, where the inner radius of the tube is to be very small, extreme care must be taken, by tedious and time consuming trial and error methods, to adjust the feathered edge of the wiping die relative to the point of tangency in order to form a satisfactory bend.

In some instances, in the forming of close radius bends, it is found that best bending results are obtained when the feathered edge is adjusted short of the tangency point to thus initiate the bend somewhat behind the tangency point. This, however, tends to introduce an irregularity, or break, or discontinuity in the transition from the straight to the curved portions of the composite tube supporting surface in the region of tangency to thus permit a deviation of the ball segments from the desired axis of curvature. On the other hand, adjustment of the feathered edge both short of and beyond the point of tangency with the rotary die, leaves the same unsupported and consequently the feathered edge becomes splintered, chipped, bent, or otherwise distorted or irreparably damaged due to the inordinate pressures applied thereto by the ball segments acting through the tube.

The tube, moreover, in the process of bending of the same, must be drawn over this feathered edge in a highly pressurized wiping action thereon. The feathered edge, accordingly, must thus provide a structurally strong, wear resistant, smooth transition surface from the straight to the circular portions of the composite die surface in order to provide and facilitate the ease of movement of the tube over and between these portions. This is a requirement which, in practice, is virtually impracticable to achieve in the use of a feathered wiping edge, particularly where tight bends are required. In practice, for example, it is frequently found that whereas the inner and outer radius portions of the bend have been executed satisfactorily, the intermediate sides of the tube are wrinkled. This is believed to be due to the fact that only the extreme tip of the feathered edge lies along the tangent where the initial wiping and bending occurs. The side portions of the tube, however, in the region of tangency, lie along and are supported by the rotary die and, hence, do not experience a wiping action as well as a bending action.

In accordance with the arrangement of the bending mechanism of the present invention, the difficulties of the prior art bending dies are obviated by provision of a composite radius block or die set comprising a unitary fixed supporting and wiping die That is to say, a continuous or unbroken tube supporting and wiping surface is provided for the tube from the region of the straight unformed portion of the tube, through the region of tangency, and on into the curved or bent portion of the tube. In this arrangement, the essential bending and wi ing action takes place along the line of tangency between the merged straight and curved surface portions of the fixed unitary die member and, hence, the feathered edge and its function in providing a supporting and wiping surface and edge, as in the prior art arrangements, is completely obviated.

The rotary die comprising the composite radius block of the present invention, however, optionally and preferably is provided with a tube supporting surface which, prior to the bending of the tube, extends substantially into the region of tangcncy of the straight and curved surface portions of the stationary die to thus initially merge with and form a continuation of the straight surface portion of the fixed die. This meeting point between the supporting surfaces of the fixed and rotary die portions, as in the prior art devices, may comprise a feathered edge, but un' like the arrangement of the prior art devices, the feathered edge of the present invention does not constitute a wiping edge for the tubing, but moves with the bent tubing over the curved surface portion of the stationary die member and away from the region of tangency where the bending of the tube is performed.

Thus it will be apparent that all of the diificulties inherent in the use of a feathered edge on the prior art wiping dies are obviated in the arrangement of the present invention, while at the same time, the advantages afforded by the use of tube supporting and conforming structure and surfaces which extend into the transition or merging point of such surfaces in the region of initial bending are retained.

Still other advantages are inherent in or flow from the construction and arrangement of the composite radius block of the present invention, as will more fully appear as the description proceeds. For example, unlike the prior art arrangements wherein the feathered edge of the fixed wiper die must be separately mounted for adjustable setting of the feathered edge relative to the point of tangcncy with the rotary die, the die members of the present invention are pivotally attached and secured together at a common pivot pin and, hence, are virtually self supporting and conveniently may be stored, one upon the other, in hinge fashion, when removed from the bending machine, or similarly stored when manufactured, packaged, or otherwise readied for shipment and sale.

In the use, moreover, of a fixed die member having a continuous unbroken supporting and wiping surface as herein employed, the same may be formed or cast of inexpensive materials such, for example, as cast iron which being, more or less porous, tends to retain the lubricant and, furthermore, when formed of a material such, for example, as Mechanite which has a graphite content, the same tends to become self lubricating.

It is an object of the present invention therefore to provide new and improved means for bending thin wall metallic tubing.

Another object is to provide a new and improved tube bending mechanism for effecting a combined bending and wiping action in a tube bending operation.

Another object is to provide a new and improved tube bending mechanism in which a combined bending and wiping action takes place on a continuous unbroken tube conforming surface.

Another object is to provide a new and improved tube bending mechanism in which the bending operation takes place on a continuous unbroken tube conforming surface and in which the initial bending occurs in the region of tangency between straight and arcuate portions of such surface.

A further object in a tube bending machine is to provide a die set, or composite radius block, comprising relatively rotatable members having a common hinged connection.

Still another object is to provide a hinged composite radius block having provision for storage of its die members in hinged fashion.

Still a further object resides in the provision of a composite radius block in which one of the die members provides a combined tube bending and wiping action in the region of tangency of a continuous unbroken surface having strai ht and curved surface portions.

Another object in a tube bending machine is to provide a hinged composite die set in which the combined bending and wiping action of a tube over a continuous straight and curved surface of one of the die members is effected upon rotation of the other of the members to which the tube is clamped.

Yet another object is to provide a composite radius block, or die sct, providing a substantially feathered edge support for a tube to be bent in which the feathered edge moves with the tubing in the process of bending the same.

Another object is to provide a composite radius block or die set in which the rotary die of the set is provided with a feathered edge to provide tube conforming and con straining support for the tube in the region of initial bending of the same.

Still another object is to provide a hinged composite radius block or die set in which the line of tangency between straight and arcuate surface portions of the fixed member of the die sct constitu es a wiping edge to effect the initial bending of a tube to be formed thereon.

Yet another object is to provide a composite radius block or die set in which the die members may be formed of inexpensive materials and by inexpensive means.

Still other objects, features, and advantages of the present invention will become more fully apparent as the description proceeds, reference being bad to the accompanying drawings wherein:

FIGS. 1 and 2 are fragmentary plan views of a conventional tube bending machine in which the bending mechanism of the machine employs a composite radius block of the present invention, FIG. 1 showing a tube prior to bending of the same on the machine and FIG. 2 showing the tube after a bend has been formed therein;

FIG. 3 is a view in elevation of the composite radius block per se, the die set members being positioned relative to each other as disclosed in FIG. 4; and

FIGS. 4 to 6 are sectional views of the composite radius block and associated parts shown in relation to a tube to be bent thereby, FIG. 4 showing the relationship of the parts prior to bending of the tube and FIGS. 5 and 6 showing the relationship of the parts when the tube has been bent respectively into 90 and bends.

Referring now to the drawings, and first more particularly to FIGS. 1 and 2, there is shown thereon, a tube bending mechanism generally designated 10 which comprises a portion of a conventional tube bending machine such, for example, as that disclosed in Patent No. 2,777,500. The machine comprises a bed 11 above which is disposed a mandrel draw rod 12 which extends substantially from end to end of the bed and into a thin wall metallic tube 13 which is to be bent from its straight form as shown in FIG. 1, into a right angular bend as shown in FIG. 2.

Tube 13 is shown positioned in supported and operative relation to the composite radius block of the present invention which is gencrnily designed by the numeral 14 and comprises a fixed die member 15 and a rotatable die member 16 which are hinged together for relative rotation about a threaded hinge pin 17 which serves to secure the composite radius block to the swing frame or bend carriage 18 of the machine, the pin 17 being aligned with the bending axis of this swing frame on the machine.

Pivot pin 17 upon being thrcadedly tigteued to the swing carriage or frame 18 clamps the die member 16 thereto for rotation therewith, and die 15 ad'litionnlly is locked against rotation with cct to the swing carriage by provision of a kcyway l9 wh formed in the under side of the die member and which receives a key provided on the swing frame 18. Die member 15 is secured as by screws 21 to a bracket 22 which, in turn, is slidably secured to a carriage 23 which may be adjustably locked in position longitudinally or transversely of guideway 24 on bed 11 by means of bolts 25 which extend through slots 26 in the carriage 23. A threaded rod arrangement 27 is provided for longitudinal adjustment of the bracket 22 relative to the carriage 23 when a prior art wiper die is employed on the machine, in lieu of composite radius block 14, and it becomes necessary to adjust the position of the feathered edge of the die relative to the point of tangency with the prior art rotary die. As aforedescribed, however, the adjustment 27 is not required in the use of the composite radius block 14 of the present invention, and bracket 22 merely serves, for the purposes, of the present to secure die member 15 against rotation about pivot pin 17. The longitudinal and transverse adjustment afforded by carriage 23 relative to the bed 11 also serve to accommodate the bending machine to such changes, in size, shape and form of the composite radius block 14 as may be necessary in forming tubes of various sizes and bend configurations.

Die members 15 and 16 are provided with semicircular grooves 28 and 29 respectively which conform to the circular cross section of the tube 13. Pressure and clamping dies 30 and 31 similarly are provided with semicircular grooves 32 and 33 respectively which likewise conform to the outer circular wall of the tube 13. Clamping die 31 is movable by a carriage 34 to which it is secured into cooperative relation with rotary die member 16 so as to clamp the tube 13 therebetween. For this purpose, carriage 34 is slidably mounted for movement along a guideway 35 provided on the swing frame 18, carriage 34 being adjustably secured to the guideway as by the bolts 36.

Pressure die 30 is removably supported as by a pair of brackets 37 to a slide block 38 which is mounted for longitudinal movement against a pair of back up rollers 39 and further supported for rolling movement along the bed by the rollers 40. Rollers 39 are carried by a carriage 41 mounted for movement along the guideway 42 of the bed 11 and adjustably secured thereto as by the bolts 43. By reason of this arrangement, pressure die 39 is urged by the carriage 41 and slide block 38 against the tube 13 to thus retain and constrain the same slidably within the groove 28 in die member 15, the arrangement being such that as the tube is drawn slidably along the groove 28 upon rotation of the swing frame 18 and the movable die member 16, the pressure die 3%, together with slide block 38, moves along with the tube, as may be seen comparatively in FIGS. 1 and 2, and also in FIGS. 4 and 5 or 6. In FIGS. 1 and 4, the right hand end surface of pressure die 30 is aligned substantially with the axis of pivot 17 and disposed generally adjacent to the confronting end surface of clamping die 31. These surfaces thus lie generally in a vertical plane which passes through the pivot axis at right angles to the tube axis. As the swing frame and the die members 16 and 31 thereon rotate about the pivot axis into the positions of FIGS. 2, 5 and 6, the confronting end surfaces of die members 30 and 31 separate angularly and die 30, in addition, moves to the right beyond the vertical plane aforesaid.

Referring now to FIGS. 3 to 6 it will be seen that die member 15 is generally of elongated configuration and terminates in a circular end portion 44 which is concentric with the axis of pin 17. Semicircular groove 28 in the die member extends along the straight portion thereof and concentrically around the circular portion 44 to the backside of the member wherein there are provided the threaded openings 45 for receiving the cap screws 21 (FIGS. 1 and 2). It may also be seen that die 16 comprises a central member 46 in which the groove 29 is formed. Die member 46 has an end portion 47 of complex configuration shaped to conform with the grooved circular portion 44 of die member 15. Thus, this end portion is shaped to conform with the semicircular cross section of groove 28 and is also shaped to conform with the circular cross section of the circular end portion 44 of die member 15 such that die member 46 has a circular or arcuate end surface 43 which matches that of the groove 28 in the circular portion 44 of die member 15. Circular surface 48 in die member 46 merges at its terminal end with the groove 29 in member 46 to form a feathered edge as at 49 which, with the parts in the positions as shown in FIGS. 3 and 4, lies at the point or line of tangency between the straight and circular or arcuate portions of groove 28 in die member 15. As may best be seen in FIGS. 5 and 6 this feathered edge 49 moves angularly away from the line of tangency which is designated 50 and lies substantially in the region of tangency between the straight and curved surface portions of groove 28 of member 15.

It will thus be seen that with the parts in the positions as shown in FIGS. 1, 3, and 4, the feathered edge 49 is positioned at the tangent 5t and thus the grooves 28 and 29 of member 15 and 16 respectively provide a composite surface support for the unformed tube 13. As otherwise expressed, the support afforded to the tube 13 by the surface 29 in die member 46 extends into the region of tangency St) in the continuous and merged straight and arcuate surface portions of the groove 28. As the tube is initially drawn and bent upon rotation of the die member 16 about the pivot axis 17, the initial wiping and bending action occurs with respect to the tangent 519 which thus serves as the wiping edge. During the initial bending, the feathered edge 4% moves away from this wiping edge where the initial bending occurs, but the groove 29, in the region of the feathered edge, nevertheless serves to constrain the tube to its desired circular cross section during this period of critical forming and bending of the tube. It will thus be clear that the feathered edge is not used as a wiping edge, as in the prior art wiping dies, and need be used optionally only with the portion 47 extending, more or less, into the region of tangency 59 in accordance with the precision of bend required in a particular case. It has been found in practice, however, that extension of the feathered edge 49 into the region of tangency 59 provides such support for thin walled tubing in the region of initial bending thereof as to make the bending of such tubes with close or tight radii of the order of ID entirely successful and practical.

Tube 13 does not move with respect to feathered edge 49 upon rotation of die member 16 to draw and wipe the tube over the groove surface 28 of member 15 and,

accordingly, the only force required to rotate the member 16 is that necessary to overcome the friction encountered in the wiping of the tube along the groove 28 and in drawing the tube internally over the mandrel 51 which is positioned within the tube and secured in a conventional manner (not shown) to the mandrel draw rod 12. Mandrel 51 comprises a plurality of ball segments 52 which gives the same a degree of flexibility sufficient to enable the mandrel to follow the bend in the tube. One or more of the segments 52 are positioned in the region of initial bending of the tube, that is, in the region of tangent 50 and, thus, the ball segments serve to maintain the circular cross section of the tube internally thereof as the initial bending and wiping of the tube occurs with respect to the line of tangency 50. The mandrel is held against movement by the mandrel draw rod 12 and, hence, as the tube is wiped, bent, and drawn relative to the tangent 5t and subsequently wrapped and simultaneously drawn about the curved portion of groove 28 in member 15, the tube is wiped internally in successive order over the remaining ball segments at the end of the mandrel. When the bend has been fully formed, the mandrel is fully withdrawn from the tube by means of the draw rod 12, as disclosed by the absence of the mandrel in FIG. 6, to thus provide a final wiping action of the ball segments internally of the tube in the region of bend thereof. It will be apparent that the smooth transition between the curved and straight portion of the groove 28 greatly facilitates both the wiping action of the tube over the surface as well as the relative movements, as aforedscribed, between the tube and the mandrel 51.

Not only are the forces required to draw and Wipe the tube and to accomplish the relative movements between the mandrel and the tube greatly reduced by the composite radius block arrangement of the present ir1- vention, but the forming of the members 15 and 46 into their grooved and arcuate configurations is greatly simplified. These die parts, moreover, may readily be formed of relatively soft materials since the bending pressures which are brought to bear are not concentrated upon a feathered wiping edge, as in the prior art, which necessitated that the feathered edge, for such purpose, be carefully machined and hardened. The die members 15 and 46, as hereindiselosed, on the other hand, may be formed of material such, for example, as cast iron which not only may be cast into the ultimate configuration desired but, in addition, will inherently provide lubrication qualities, or adaptabilities for application of lubricants to facilitate the wiping action of the tube thereon.

The die member 46 is secured between two plates 53 and 54 and held and secured in assembled relationship therewith as by the dowel pins 55 and the cap screws 56. Plate 53 has an opening (FIG. 3) concentric with the arcuate surface 48 in die member 46 for receiving the threaded end portion of pin 17, and this opening is enlarged as at 58 in the region of keyway 19 to receive a washer 59 which is received in supporting relation on the upper surface of swing frame 18. Plate 54 likewise has an opening 60 concentric with the arcuate surface 48 of die member 46, and this opening is adapted to receive the opposite end of pin 17 which is also threaded.

The side of pin 17 adjacent plate 54 is enlarged as at 61 to provide a shoulder for support of the plate, and the pin is further enlarged as at 62 adjacent to the plate 53 to thus provide a shoulder for plate 53. By this means, the end or hinge portions of plates 53 and 54 are held in spaced relation in hinge fashion relative to die member 15 when the pin 17 is secured to the bending machine and the nut 64 and its lock nut 65 are drawn up sutficiently to lock the plates 53 and 54 to their respective shoulder supports. It will be noted that the pin 17 is provided with a screwdriver slot 66 by which the pin may be threadedly advanced into the swing frame prior to tightening of the nuts 64 and 65, and that a washer 67 preferably is provided between the nut 64 and plate 54.

The circular portion 44 of die member 15 has a central opening for receiving the central and enlarged portions 61 and 63 respectively of pin 17 with which it is freely relatively rotatable such that the die member 16 together with pin 17 to which it is clamped may move freely with respect to the die member 15. For this purpose, member 15 is so shaped and formed as to provide a close but freely rotatable relation with and between the spaced plates 53 and 54.

By reason of the hinged construction and arrangement of die members 15 and 16, the same may be stored one upon the other in hinged fashion as best shown in FIG. 6, from which it may be seen that the member 46 may be moved into engagement with the backside of member 15. In this position, the side plates 53 and 54 are moved into enclosing relationship with respect to the sides of member 15 to thus ideally compact the dies for storage, shipment, and the like.

Referring again to FIGS. 1 and 2, it will be seen that plate plate 54 is provided With a peripherally extending notch 68 for receiving a pin 69 which is carried by the member 15. In FIG. 1, pin 69 engages one end of notch 68 to PYcVfint fufthfir t k IOifltion of the die mem- 8 her 16 with respect to the die member which would tend to move the feathered edge 49 beyond the tangent and thus damage the same and/or the groove 28 in die In FIG. 2, the pin engages the other end of the notch to prevent a bending of the tube beyond the intended 99 bend to be performed therein.

From the foregoing, the operation of the composite radius block of the present invention, in conjunction with the conventional tube bending machine disclosed therewith, should now be apparent and it will sutlice therefore merely to point out, by way of summary, the principal actions which take place on the tube during a bending operation performed thereon by relative rotation of the die members 15 and 16. Tube 13, being clamped at the end thereof to rotary die member 16, is drawn thereby ver the grooved surface 28 of die member 15 as die member 16 is rotated, for example, from its position of PEG. 1 into its position of FIG. 2. In this drawing action of tube 13 over groove surface 23, the same is simultaneously wiped and initially bent with respect to line of tangency between the straight and curved surface portions of groove 28 which thus serves as a wiping edge in the sense of the prior art wiping dies. Subsequent to the initial bending and wiping, the tube is also wrapped about and simulta cously wiped over the curved portion of groove in the region of the circular portion 44 of die member 15. This circular portion extends through an arc in excess of 180 such that the bend in the tubing upon continued rotation of the die member 16 may be of the order of 189 as in FIG. 6 or 90 as in FIGS. 2 and 5.

The wiping edge inherently present in the region of tangency of groove 23 in die member 15 need not be adjusted relative to the rotary die to establish a region of tangency therewith, as in the prior art wiper dies and, hence, the function of the mandrel segments in maintaining the circular cross section of the tubing in the region of initial bending is augmented by the smooth transition from the straight to the curved portions of wiper surface 28 in their region of tangcncy. The cooperative action of pressure die with die 15 in this region of "agency, moreover, serves to constrain the outer surface of the tube to its circular cross section in this region of initial bending, as does the feathered edge portion of rotary die member 46 and its coacting clamping die 31. Although the feathered edge may extend initially into the region of tangency of the wiping groove 28, it is not subjected to the extreme bending forces which are brought to bear on the tangent wiping edge of this groove and moves out of the region of initial bending as continued rotation of the swing frame talres place. This feathered edge, being a portion of the rotary die 16, rotates therewith and maintains a fixed tangential relationship with respect to the curved portion of groove 28 and, hence, need not be adjustable with respect thereto.

A composite radius hie-cl; as thus been provided which is well adapted to fulfil the aforcstated. objects of the invention and while a single embodiment thereof has been disclosed, it will be apparent that various changes may be made without departing from the spirit or scope of the invention. For example, the die member 15 and hinge portions of pin 17 may be formed integrally in order to reduce the diameter of the circular or arcuate portion of groove 23 to thus permit the bending of tubing of very small diameter.

This invention may thus be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The pres ent embodiment of the invention is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Having thus described my invention, what I claim as 3,1 rates new and useful and desire to secure by Letters Patent is:

1. A composite radius block of the character disclosed for forming wrinide free tight bends in thin Wall metallic tubing comprising a pair of hinged dies, one of said dies having an elongated tube supponting straight portion adapted for rigid attachment at one end thereof to a tube bending machine and terminating at the other end in a circular tube forming portion, said straight and circular portions having a common groove providing a continuous unbroken surface of circular cross section conforming to one half that of a tube to be bent on the machine, said groove extending in a continuous unbroken surface along said straight portion and around said circular portion to the back side of said straight portion, and said straight surface portion of the groove being tangent to said circular surface portion thereof whereby a tube portion slidably urged and constrained against said continuous grooved surface in said tube supporting straight portion and drawn by a clamped adjacent tube portion about said continuous grooved surface in said tube forming circular portion in a combined sliding, wiping, and Wrapping action thereabout is constrained to follow said circular cross section throughout the region of bend of the tube Without introducing wrinkles and like distortions in the sidewall of the tube, the other of said dies comprising an elongated straight member for supporting said clamped adjacent tube portion and having a groove therein conforming in cross section to that of said first named groove, a pair of side members secured respectively to opposite sides of said straight member and terminating in circular portions having said circular portion of said one of the dies extended therebetween and hinged thereto.

2. A composite radius block as in claim 1, said groove in said straight member terminating in a feathered edge at the hinged end of the member and said groove extending tangent to said circular surface portion of the common groove in said one of the dies, said feathered edge extending into the region of tangency of the straight and circular portions of said common groove when said straight member is positioned in extended alignment with said straight portion of said one of the dies.

3. A composite radius block as in claim 1 and comprising a hinge pin for pivotally connecting the dies together and to said bending machine.

4. A composite radius block as in claim 1, said straight portion and said straight member respectively of said hinged dies having the same width and a combined thickness equal approximately to the diameter-of said circular portion of said one of the dies and being foldable one upon the other in stored relation with said side members moving into enclosing relation with respect to said straight portion of said one of the dies.

5. A composite radius block as in claim 4, said dies having complementary means for limiting relative rotation therebetween from said folded stored relation thereof to an open position in which the groove in said straight member and the straight surface portion of said common groove extend mutually in a straight line and meet in the region of tangency of said straight and circular portions of the groove in said one of the dies.

6. In a tube bending machine of the character disiii closed having a bed and a swing frame, a first die having an elongated tube supporting straight portion de tachably secured at one end thereof to said bed of the machine, said straight portion terminating at the other end thereof in a tube forming circular portion disposed concentrically with the axis of said swing frame of the machine, said straight and circular portions having a common groove providing a continuous unbroken surface of circular cross section conforming to one half that of a tube to be bent on the machine, said groove extending in a continuous unbroken surface along said straight portion and around said circular portion to the back side of said straight portion, and said straight surface portion of the groove being tangent to said circular surface portion thereof whereby a tube portion slidably urged and constrained against said continuous grooved surface in said tube supporting straight portion and drawn by a clamped adjacent tube portion about said continuous grooved surface in said tube forming circular pontion in a combined sliding, wiping, and wrapping action thereabout is constrained to follow said circular cross section throughout the region of bend of the tube without introducing wrinkles and like distortions in the sidewall of the tube, a second die comprising a center member for supporting said clamped adjacent tube portion and side members secured to said center member and hinged to said circular portion of the first die concentrically therewith, said center member having a straight groove therein of cross section corresponding to that of said common groove of the first die, a hinge pin pivotally securing said first and second dies together and for clamping said center member to the swing frame of the machine, a pressure die mounted on said bed of the machine for slidably urging said tube portion against said straight portion of the first die, and a clamping die mounted on said swing frame of the machine for clamping said adjacent tube portion to said center member of the second die, said pressure and clamping dies respectively having grooves complementary to those of said first and second dies.

7. The combination in a tube bending machine as in claim 6, said groove in said first die comprising a continuous sliding surface for support of said tube and providing a wiping edge therefor in the region of tangency of said straight and circular surface portions of the groove, said groove in said center member of the second die extending tangent to said circular surface portion of the first die and terminating at or near said surface.

8. The combination in a tube bending machine as in claim 6 and further comprising a mandrel secured to said machine and terminating in a flexible end portion which extends into the tube into the region of tangency of said straight and surface portions of said common groove.

References Cited in the file of this patent UNITED STATES PATENTS 87 8,604 Brinkman Feb. 11, 1908 1,174,143 Heinen Mar. 7, 1916 1,238,941 Reynders Sept. 4, 1917 1,575,928 Mueller et al. Mar. 9, 1926 1,650,955 Miller Nov. 29, 1927 

1. A COMPOSITE RADIUS BLOCK OF THE CHARACTER DISCLOSED FOR FORMING WRINKLE FREE TIGHT BENDS IN THIN WALL METALLIC TUBING COMPRISING A PAIR OF HINGED DIES, ONE OF SAID DIES HAVING AN ELONGATED TUBE SUPPORTING STRAIGHT PORTION ADAPTED FOR RIGID ATTACHMENT AT ONE END THEREOF TO A TUBE BENDING MACHINE AND TERMINATING AT THE OTHER END IN A CIRCULAR TUBE FORMING PORTION, SAID STRAIGHT AND CIRCULAR PORTIONS HAVING A COMMON GROOVE PROVIDING A CONTINUOUS UNBROKEN SURFACE OF CIRCULAR CROSS SECTION CONFORMING TO ONE HALF THAT OF A TUBE TO BE BENT ON THE MACHINE, SAID GROOVE EXTENDING IN A CONTINUOUS UNBROKEN SURFACE ALONG SAID STRAIGHT PORTION AND AROUND SAID CIRCULAR PORTION TO THE BACK SIDE OF SAID STRAIGHT PORTION, AND SAID STRAIGHT SURFACE PORTION OF THE GROOVE BEING TANGENT TO SAID CIRCULAR SURFACE PORTION THEREOF WHEREBY A TUBE PORTION SLIDABLY URGED AND CONSTRAINED AGAINST SAID CONTINUOUS GROOVED SURFACE IN SAID TUBE SUPPORTING STRAIGHT PORTION AND DRAWN BY A CLAMPED ADJACENT TUBE PORTION ABOUT SAID CONTINUOUS GROOVED SURFACE IN SAID TUBE FORMING CIRCULAR PORTION IN A COMBINED SLIDING, WIPING, AND WRAPPING ACTION THEREABOUT IS CONSTRAINED TO FOLLOW SAID CIRCULAR CROSS SECTION THROUGHOUT THE REGION OF BEND OF THE TUBE WITHOUT INTRODUCING WRINKLES AND LIKE DISTORTIONS IN THE SIDEWALL OF THE TUBE, THE OTHER OF SAID DIES COMPRISING AN ELONGATED STRAIGHT MEMBER FOR SUPPORTING SAID CLAMPED ADJACENT TUBE PORTION AND HAVING A GROOVE THEREIN CONFORMING IN CROSS SECTION TO THAT OF SAID FIRST NAMED GROOVE, A PAIR OF SIDE MEMBERS SECURED RESPECTIVELY TO OPPOSITE SIDES OF SAID STRAIGHT MEMBER AND TERMINATING IN CIRCULAR PORTIONS HAVING SAID CIRCULAR PORTION OF SAID ONE OF THE DIES EXTENDED THEREBETWEEN AND HINGED THERETO. 